Elevator system

ABSTRACT

An elevator system including a structure having a plurality of landings, an elevator car, a drive motor for moving the car relative to the structure to serve the landings, and control apparatus for controlling the drive motor. The control apparatus includes an acceleration transducer which provides a substantially ripple-free stabilizing signal responsive to acceleration by detecting the rate of change of the counter emf of the drive motor. The circuit in which the stabilizing signal is developed is devoid of metallic connection to the drive motor circuit, permitting its use with a solid state source of direct current potential, as well as with a rotating source.

United States Patent 1 Caputo.

[ 41 ELEVATOR SYSTEM" William R. Caputo, Wyclgoff, NJ.

[73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa;

[22] Filed: May 24, 1972 [21] Appl. No.: 256,318

[75] Inventor:

52 us. Cl. 187/29, 318/331 3,552,524 Benjamin et al 187/29 CONVERTER I CURRENT RECTIFIER RATOR sp 1 July 31, 1973 Primary Examiner-Gene Z. Rubinson Attorney- A. T. Stratton and Donald R. Lackey 571 7 ABSTRACT An elevator system including a structure having a plurality of landings, an elevator car, a drive motor for moving the car relative to the structure to serve the landings, and control apparatus for controlling the drive motor. The control apparatus includes an acceleration transducer which provides a substantially ripple-free stabilizing signal responsive to acceleration by detecting the rate of change of the counter emf of the drive motor. The circuit in which the stabilizing signal is developed is devoid of metallic connection to the drive motor circuit, permitting its use with a solid state source of direct current potential, as well as with a rotating source.

33 Claims, 4 Drawing Figures ELEVATOR SYSTEM BACKGROUND OF THE INVENTION l. Field of the Invention The invention relates in general to elevator systems, and more specifically to control apparatus for the drive motor associated. with the elevator car of an elevatorsystem, including a stabilization transducer which provides a stabilizing signal'proportional to acceleration. of the car.

2. Description of the Prior Art High speed elevator systems driven. by a direct current motor, with a tachometer as'the feedback control element to control the velocity of the elevator car, require stabilization means in order to achieve a smooth response. The derivative of the drive motor armature voltage, or the derivative of the counter emf developed by the armature of thedrive motor, maybe used as the stabilizing signal when metallic connections between the control circuit and the armature circuit of the drive motor can be-tolerated, and the ripple frequencies in these voltages can be filtered out. When the drive motor is driven directly from the alternating source via solid state switching devices, such as witha single or dual converter whichincludes thyristor switching devices, conductor continuity between thee control circuit and the armature circuit of the drive motor may not be desirable,and indeed may not even be-allowable. Further, filtering the high frequency alternating component may actually cause instability.

The ideal solution would be to develop the stabilizing signal by taking the derivative of the tachometer voltage, but tachometers with sufficiently low ripple are not available. Tachometers produce electrical noise in their output signals due to slots, commutator bars, brushes, imperfections in construction, and the gearing or belting of the drive coupling. This electrical noise I appears as an unwanted. addition to thee command signal. The elevator car is capable of responding'to this SUMMARY OF THE INVENTION Briefly, the present invention is a new and improved elevator system which includes control apparatus which develops a stabilizing signal proportional to the rate of change of counter emf developed by the elevator car drive motor. The counter emf developed by the winding of the armature of the drive motor is directly related to acceleration. The means for developing the stabilizing signal inherently cancels any ripple which may be present in the direct current voltage applied to the armature of the drive motor, without any additional filtering, and there is no conductor continuity from the circuit which develops the stabilizing signal to the armature circuit of the drive motor.

More specifically, the control apparatus of the elevator system includes an acceleration transducer for developing a stabilizing signal statically and electromagnetically which, in a preferred'embodiment of the invention, includes first, second and third electromagnetically coupled windings. The first winding is a current winding, connected inseries with the armature of the drive motor; The second winding is a voltage winding, which is disposed" to develop a magnetomotive force in opposition to that developed by the first winding. The second winding is connected across the serially connected armature andfirst winding in a circuit which includes predetermined magnitudes of inductance and resistance. Thesemagnitudes are selected sucli that the total inductance and total resistance of this circuit have substantially the. same ratio to the totalv inductance and total resistance, respectively, of the armature circuit, as the ratioof the turns'in the second winding to the turns in the first winding. This arrangement cancels any ripple component present in the magnetic flux of each circuit, and the resultant ripple-free flux' which links the third winding is proportional to the rate of change of counter emf, which is directly related to acceleration. The signaldeveloped in the third winding is used as the stabilizing signal in the control loop.

BRIEFDESCRIPTION OF THE DRAWINGS FIG. 21 is a graph which plots a speed reference signal and an acceleration stabilizing signal versus time;

FIG. 3- is an end view of an acceleration transducer constructed according to the teachings of the inven tion; and

FIG. 4 is a partial sectional view of the acceleration transducer shown in FIG. 3, taken in thee direction of arrows IV-IV and substantially along the broken line which interconnects the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and FIG. 1 in particular, there is shown an elevator system 10 which includes a direct current drive motor 12' having an armature 14 and a field winding 16. The armature 14 is electrically connected to an adjustable source of direct cursystems which use a motor generator set as the source of direct current potential.

The dual converter 18 includes first and second con-- verter banks I and II, respectively, which may be threephase, fullwave bridge controlled-rectifiers connected in parallel opposition. Each converter includes a plurality of controlled rectifier devices 20 connected to interchange electrical power between alternating and direct current circuits. The alternating current circuit ineludes a source 22 of alternating potential and busses 24, 26 and 28, and the direct current circuit includes busses 30 and 32, to which the armature 14 of the direct current motor 12 is connected. The dual bridge converter 18 not only enables the magnitude of the direct current voltage applied to armature 14 to be adjusted, by-controlling the conduction or firing angle of the controlled rectifier devices, but it allows the direction of the direct current flow through the armature 14 to be reversed when desired, by selectively operating the converter banks. As illustrated, when converter bank I is operational, current flow in the armature 14 would be from bus 30 to bus 32, and when converter bank 11 is operational, the current flow would be from bus 32 to bus 30.

The field winding 16 of drive motor 14 is connected to a source 34 of direct current voltage, represented by a battery in FIG. 1, but any suitable source, such as a single bridge converter, may be used.

The drive motor 12 includes a drive shaft, indicated generally by broken line 36, to which a traction sheave 38 is secured. An elevator car 40 is supported by a rope 42 which: is reeved over the traction sheave 38, with the other end of the rope being connected to a counterweight 44. The elevator car is disposed in a hoistway 46 of a structure having a plurality of floors, such as floor 48, which floors are served by the elevator car 40.

The movement mode of the elevator car 40, and its position in the hoistway 46, are controlled by the voltage magnitude applied to the armature 14 of the drive motor 12. The magnitude of the direct current voltage applied to armature 14 is responsive to a velocity command signal V provided by a suitable speed pattern generator 50. The servo control loop for controlling the speed, and thus the position of car 40 in response to the velocity command signal V may be of any suitable arrangement, with a typical control loop being shown schematically in FIG. 1.

A signal V responsive to the actual speed of motor 12 is provided by a tachometer 52, which is belted, geared, or otherwise mechanically coupled to the shaft 36 of the drive motor. A comparator 54 provides an error signal V responsive to any difference between the velocity command signal V and the actual speed of the motor 12, represented by signal V When a tachometer is used as the feedback means to control velocity in a high performance elevator system, stabilization means is mandatory for achieving a smooth response. The derivative of the voltage applied to the armature 14, or the derivative of the counter emf developed by the armature 14, may be used when conductor continuity between thecontrol circuitry and the armature 14 can be tolerated, and the high frequencies in these voltages can be filtered out without introducing additional instability into the control loop. With a dual converter 18 as the source of unidirectional potential, there is no isolation between the source 22 of alternating potential and the armature 14, and thus conductor continuity between the armature l4 and the control circuits is usually prohibited. Furthenwith a 60 Hertz, three-phase source 22, and a full-wave bridge con verter, a strong 360 Hertz ripple is present in the armature applied voltage, which would be undesirable if allowed to enter the control circuit without substantial attenuation. The derivative of the tachometer voltage is also not suitable, due to electrical noise in the tachometer output, which when the derivative thereof is taken, may appear as a stronger signal than the rate of change of the desired signal.

The control circuit of the disclosed elevator system is stabilized, according to the teachings of the invention, by deriving a signal proportional to the rate of change of the counter emf developed by the drive motor 12, which is directly related to acceleration. The signal developedaceording to the invention is substantially noise-free, and it requires no conductor continuity to the armature 14,

More specifically, an acceleration transducer 60 is provided which, in a preferred embodiment of the invention, includes first, second and third windings 62, 64 and 66, respectively, which'are electromagnetically coupled via a magnetic core 68.

The first winding 62, which may be called a current winding, is preferably one turn, or less, as will be hereinafter explained. The first winding 62 is serially connected in a first circuit 70 which includes the armature 14 of the drive motor 12. Winding 62 includes electrical leads MA] and GAl, with lead MAl being connected to the armature 14, and lead GAl connected to bus 32. The flux produced in the magnetic core 68 due to current flowing through winding 62 will be proportional to the armature applied'voltage V A i.e. the'voltage output of the converter 18, less the counter emf voltage V developed by the armature 14, less the voltage e, across winding 62, divided by the impedance of the first circuit, which includes its total resistance and inductance. This flux will include the ripple component produced by the switching of the solid state switching devices of the converter 18.

The second winding 64 is connected in a second circuit 72 which, similar to the first circuit 70, is connected between busses 30 and 32. Thissecondcircuit 72 is designed to have a predetermined relationship with the first circuit 70, such that fluxes produced by the first and second windings due to the armature applied voltage V, and its ripple component may balance one another and thus be cancelled by directing the fluxes from the two windings in opposite directions through a winding leg of the magnetic core 68. The resultant flux will be substantially ripple-free, and proportional to the counter emf V Any change in the counter emf will produce a voltage in the third winding 66 which is proportional to the rate of change of counter emf, which is directly related to acceleration.

For a perfect balance between the first and second circuits 70 and 72, respectively, in which the first and second windings 62 and 64 are disposed, the following relationships should be achieved:

N2/Nl 1.2/1.1 =6 R2/Rr where:

N1 is the numberof turns in the first winding 62 N2 is the number of turns in the second winding 64 L1 is the total inductance of the first circuit 70 L2 is the total inductance of the second circuit 72 R1 is the total resistance of the first circuit 70 R2 is the total resistance of the second circuit 72. For practical purposes, the total inductance of the second circuit may be made somewhat smaller than the computed value, in order to reduce the size of the inductor which is added to the second circuit. Reducing the total inductance of the second circuit allows a certain portion of the ripple component to appear in the resultant flux, but a small ripple component signal is not a serious disadvantage to the operation of the control circuitry. I

More specifically, the second winding 68 is serially connected with'an inductor 74 and a resistor 76 between busses and 32, and a resistor 78 is connected across inductor 74. Winding 64 includes a lead AF] which is connected to inductor 74, and it also includes a lead GAI' which is connected to .bus 32. The values of resistors 76 and 78 and inductor 74 are all selected to achieve the ratio N2/Nl for R2/Rl and L2/Ll, or as close to this ratio as practical, as hereinbefore stated. The flux produced in the magnetic core 68 due to current flowing through winding '64 is proportional to the armature applied voltage V, plus the voltage e across winding 64, divided by the impedance of the second circuit 72, which includes the total resistance and the total inductance of this circuit. This flux, similar to the flux produced by the first winding 62, includes the ripple component produced by the switching of the solid state switching devices in the converter 18.

As illustrated by the dots at the ends of windings 62 and 64, the magnetomotive force developed by the winding 62in the magnetic core 68 opposes the magnetomotive force developed by winding 64 in the magnetic core 68. Thus, the effect of thev armature applied voltage V along with its ripple component, is substantially cancelled, with the resulting flux being proportional to the counter emf developed by the armature 14 of the drive motor 12. Any change in the counter emf thus generates a voltage V in the pickup winding 66,

which winding has leads AFB and PSC.

The voltage V is applied as a negative feedback signal to the closed control loop, stabilizing the signal V Signals V and V are applied to a summing circuit 80 with the algebraic signs illustratedin FIG. 1, in order to provide a stabilized error signal V The stabilized error signal V may be amplified in an amplifier 82, and dependingupon the specific control loop utilized, the amplified signal may be compared with a signal V in a comparator 86, with signal V being responsive to the current supplied to the dual converter 18. Signal V maybe provided by any suitable feedback means,

. such as by a current transformer arrangement 84 disposed to provide a signal responsive to the magnitude of the alternating current supplied by the source 22 to the converter 18 via busses 24, 26 and 28, and a current rectifier 88 which converts the output of the current transformer arrangement 84 to a direct current signal V As disclosed in co-pending application Ser. No. 238,917, filed Mar. 28, 1972, which is assigned to the same assignee as the. present application, amplifier 82 may be a switching amplifier which is responsive to the polarity of the input signal to enable the unidirectional signal V to be used regardless of the polarity of the'input signal V Signal V and the amplified signal V, are compared in a comparator 86 to provide a signal V, responsive to any difference, which signal is applied to a phase controller 90. Phase controller 90, in response to timing signals from busses 24, 26 and 28 and the signal V provide phase controlled firing pulses for the controlled rectifier devices of the operational converter bank. The hereinbefore mentioned co-pending application Ser. No. 238,917 discloses a phase controller which may be used for the phase controller 90 shown in FIG. 1.

While in the preferred embodiment of the invention the stabilizing signal V has been described as being developed in a winding 66, it is to be understood that the output winding 66 may be replaced by any suitable magnetic'field sensing means. For example, the magnctic field sensing means may include a Hall Generator, and means for differentiating its output signal. FIG. 2 is a graph which plots the speed signal V and the stabilizing acceleration signal V versus time. When the elevator car is to move, the speed signal V provides a first transition signal 92 between zero speed 94 and a constant acceleration portion 96 of the signal. The acceleration signal V decreases from zero 98 very rapidly during a portion 100 of the signal which corresponds to the first transition portion 92 of the speed signal vsp, and "then changes to a constant negative portion 102 while constant acceleration is called for by the speed signal. A second curved transition occurs at portion 104 of the speed reference pattern V as the speed signal changes from constant acceleration 96 to constant speed and zero acceleration at 99, with the acceleration signal dropping rapidly during this second transition along portion 106 of the signal, back to zero I When the elevator car is requested to decelerate, a third curved transition 108 occurs between constant speed 99 and constant deceleration 110, with the accelsition. The acceleration signal V becomes a constant positive value, indicated at 114 during the constant deceleration 110, and then the speed reference pattern Vsp enters a fourth curved transition portion 116 which directs the car speed between the constant deceleration mode to zero speed indicated at 94?. The acceleration signal V drops rapidly along portion 118 of the signal during this fourth transition, back to zero 98". The negative feedback provided by the acceleration signal V enables the control loop to anticipate the changing speed signal and smooth the system response.

FIG. 3 is an end view of an'acceleration transducer 60' which may be used for the acceleration transducer 60 shown in FIG. 1, and FIG. 4 is a partial crosssectional view of the transducer60 shown in FIG. 3, taken in the direction of arrows IV-IV, and substantially along the broken line which interconnects the ar-' a winding leg 120 and a return path. The return path of the winding leg also functions as the casing or enclosure of the transducer 60', and it includes a side wall portion 122 which is preferably cylindrical, as shown, having an opening which extends between the ends thereof, and first and second end portions 124 and 126, respectively, which close the ends of the side wall portion 122 to define a closed chamber or cavity 128. The winding leg 120 extends coaxially through the cavity and is suitably fixed to the first and second end portions 124 and 126.

The winding leg 120 k includes at least one nonmagnetic gap therein selected to maintain the magnetic core well below the saturation level. Four nonmagnetic gaps 130, 132, 134 and 136 are shown in the specific embodiment of FIG. 4, with gaps and 136 being disposed between the ends of the winding leg 120 and the adjacent end portions 124 and 126, respectively, and gaps 132 and 134 are disposed within the winding leg 120.

The disclosed construction of the magnetic core 68 provides an enclosure for the acceleration transducer 60' which completely shields the windings thereon from surrounding magnetic fields, enabling the transducer to be placed in what would otherwise be a hostile environment. When the source of adjustable unidirectional potential is a dual bridge converter, the rapidly changing magnetic fields produced by the switching of a source potential would be detrimental to the accuracy of the acceleration transducer, if it were not adequately shielded from these changing magnetic fields. The disclosed construction of the magnetic core also gives the transducer fractional turn capability, the advantage of which will be hereinafter explained.

First, second and third windings, which may also be referred to as'current, voltage and pickup windings 62', 64' and 66', respectively, are disposed in inductive relation with the winding leg 120. The current winding 62 corresponds to the winding 62 shown in FIG. 1, which is connected in serieswith the armature 14 of the drivemotor 12. The voltage winding 64 corresponds to the winding 64 shown in FIG. 1, which is connected in series with the resistors and inductors required by the specific application. The pickup winding 66' corresponds to the winding 66 shown in FIG. 1, which develops the stabilizing signal. The pickup winding 66 is preferably disposed between the, current voltage windings 62' and 64', and electrostatically shielded from these windings by suitable electrostatic shield members 140 and 142. Shield members 140 and 142 may be thin, disk-shaped members formed of copper or aluminum, sized to snugly fit the cavity 120, and they each may include an electrical lead, or other means, for connecting the shield members to ground. Shield members 140 and 142 are radially slotted to prevent them from acting as a shorted turn. The electrostatic shielding is necessary since the voltage associated with the voltage coil 64' is rapidly switching between large voltage magnitudes, when the adjustable voltage source is a solid state converter, which would set up electrostatic fields and capacitively couple electrical noise into the pickup coil 66'. The grounded shield members 140 and 142 minimize such capacitive coupling.

The electrical leads connected to the windings 62', 64 and 66 may all be brought out through one end of the transducer 60', if desired, such as through the first end 124, through suitably insulated openings disposed through the end portion. The electrical leads AFB and PCS attached to the pickup coil 66' are preferably shielded, such as with a braided shield member 146, and the shield 146 is connected to ground. As illustrated, the shielded leadsAFB and PSC may be brought through an opening 154 in end 124. v

The current winding 62' is disposed immediately adjacent end 124, with its electrical leads MAI and GA] extending through insulated openings 150 and 152 in the first end 124.

The electrical leads from the voltage winding 64 may be brought through the same opening 154, as the leads from the pickup winding 66, if desired.

Since elevator drive motors cover a considerable range in electrical ratings, depending upon the specific application, it would at first appear that an acceleration transducer would have to be developed for each rating.

It has been found, however, that with the disclosed construction of the acceleration transducer 60 that the current winding 62' has fractional turn capability. Thus, in an application wherein the number of ampere turns would be too high for a given size of transducer, it is possible to reduce current winding 62' to a fraction of a turn. The transducer 60' was constructed using different fractions of a turn for the current winding 62' and in every instance the effective fractional turn which resulted was equal to the angular displacement between the entering and exiting openings of the electrical leads attached to the current winding. Thus, the effective fractional turn of the current winding shown in FIG. 3 would be equal to 360 less the angle between the leads MAl and GA] which angle is indicated in FIG. 3 by the reference numeral 160.

The exact reason for the accurate relationship between the angular displacement hereinbefore mentioned. and the effective fractional turn is not entirely understood, but it is believed to be due to the construction of the magnetic core 68' wherein the winding leg is completely surrounded by the return path for the winding leg. Thus, instead of thinking of the current winding 62 as a fraction of a turn, although it functions as such, it more accurately may be thought of as a single turn which links a predetermined portion of the magnetic circuit, with the predetermined portion depending upon the specific portion of a complete turn which is utilized for the current winding. The current winding 62' provides a certain amount of flux, part of which goes through the winding leg 120 and part of which does not, i.c. part goes through the outer shell of the enclosure without passing through the winding leg. The amount which passes through the winding leg depends upon the fraction of a complete turn selected for the current winding 62'.

The fractional turn capability of the current winding 62 facilitates the manufacture and assembly of the acceleration transducer for different ratings of electrical drive motors. For example, the voltage winding 64' and r the pickup winding 66' may be assembled with portions 120 and 120", respectively, of winding leg 120, and with shield member 142. Portions 120' and 120" of the winding leg 120 may be pre-assembled by fastening means 162. lnsulating spacer means 164may be disposed against the inner surface of the second end 126, and the pre-assembled portions 120' and 120" of the winding leg, and windings 64' and 66', may be disposed within the cavity 128 defined by the outer portion 122 of the magnetic core 68. A suitable liquid potting material may then be introduced into the cavity which is gelled and cured to a solid, to firmly secure the windings within the cavity. An epoxy resin system has been found to be suitable for the potting material, but other resins may be used.

Up to this point, the acceleration transducer 60' may be used for a number of different ratings of drive motors. It is only necessary to select the proper size of current winding, and a first end 124 which has the openings 152 and 154 disposed at the angular locations which are required to accommodate the specific angular displacement of the leads MAl and GAl attached to the current winding. The current winding 62' is disposed about a portion 120" of a winding leg 120, which portion is fixed to the inner side of the end portion 124. The shield member may be fixed to the outwardly extending end of winding leg portion 120".

An opening is disposed through the shield member 140 to accommodate theleads from windings 64' and 66'.

In summary, there has been disclosed a new and improved elevator system which includes an elevator car, a drive motor, and a control system for directing the movement of the elevatorcar without jitter due to electrical noise in the stabilizing signal applied as a negative feedback in the control loop. A signal proportional tov the rate of change of the counter emf developed by the drive motor is provided, which is substantially free of any ripple component which may be included with the unidirectional voltage applied to the armature of the drive motor- The rate of change of adjustable voltage source.

counter emf is directly related to the acceleration of I the drive motor, and thus the acceleration of the car. This acceleration responsive stabilizing signal is developed without conductor continuity between the control circuitry and the armature of the drive motor, enabling the transducer to be used on elevator systems which utilize solid state static converter apparatus, as well as on those systems which use a motor generator set as the source of adjustable direct current potential. The filteringaction of the disclosed acceleration transducer removes the ripple component frorn'the source of direct current without resorting to'capacitors and inductors, which may in themselves add instability to the system. The inherent filtering action is the result of developing two opposing fluxes each, of which contain. the ripple component, with the resultant flux being substantially free of 'the ripple component. The disclosed acceleration transducer also lends itself to assembly and manufacture, as'only the current winding need be tailored to "the specific application, due to the fractional turn capability of the current winding, which provides the ampere turn adjustment required for different applications. I

I claim as my invention: 1. An elevator system, comprising an elevator car, I l a structure having spaced landings to be served by said car, motor means including an armature, said motor means moving the car relative to said structure to serve the landings, means providing a speed patternreference signal, first feedback means providing a first feedback signal, said first feedback-signal being responsive to the speed of the car, 1 meanscomparing the speed pattern reference signal with the first feedback signal to provide an error signal responsive to any difference, means stabilizing said error signal, including second feedback means, said second feedback means providing a negative feedback signal responsive to the rate of change of the counter emf of 'saidmotor means, j said second" feedback means developing said negative feedback signal statically and electromagnetically, without conductor continuity to the armature of the motor means, and means providing an adjustable voltage source responsive to said stabilized error signal, said motor means being connected to said adjustable voltage source. i 2. The elevator system of claim 1 wherein the means providing the adjustable voltage source providesa unidirectional voltage with a ripple component, with the 3. The elevator system of claim 2 wherein the second feedback means includes means providing a first flux responsive to the adjustable voltage source and the counter emf, means providing a second flux responsive to the adjustable voltage source, and means combining the first and second fluxes to provide a substantially ripple-free resultant flux responsive to the rate of change of the counter emf.

4. The elevator system of claim 2 wherein the means providing the adjustable voltage source is a converter having static switching devices.

5. The elevator system of claim 1 wherein the second feedback means includes first and second windings disposed in inductive relation with a magnetic core, and magnetic field sensing means, said first winding being connected in a first circuit which includes the first winding connected in series with the armature of the motor means across the adjustable voltage source, said second winding being connected across the adjustable voltage source in a second circuit which includes we determined values of inductance and resistance, said magnetic field sensingmeans being disposed to develop an output voltage responsive to a changing difference between the fluxes developed in the magnetic core by said first and second windings.

6. The elevator system of claim 5 wherein the magneticfield sensing means is a third winding disposed in 1 v inductive relation with the magnetic core.

7. The elevator system of claim 5 wherein the predetermined values of inductance and resistance in the circuit of the second winding are selected such that the total inductance and total resistance of the second circuit have substantially the same ratio to the total inductance and total resistance, respectively, of the first circuit, as the turn ratio of the second winding to the first winding.

8. The elevator system of claim 5 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposed between the first and second end portions about which the first and second windings are disposed.

9. The elevator system of claim 8 wherein the magnetic field sensing means is a third winding, with said third winding being disposed about the winding leg.

10. The elevator system of claim 7 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposed between the first and second end portions about which the first and second windings are disposed, and wherein the first winding is a predetermined fraction of one turn, with, this fractionbeingused to establish theratio whichguides the selection of the values of inductance andresistance in the second circuit.

11. The elevator system of claim 10 wherein the first winding includes electrical leads disposed to enter the chamber of the magnetic core through openings in a predetermined end thereof, with the first winding following a predetermined arcuate path between the electric leads, having a length responsive to the angular displacement of the leads, which angular displacement de-- termines thee specific fraction of a turn in the first winding.

12. The elevator system of claim 8 wherein the magnetic field sensing means is a third winding, said third winding being disposed between the first and second windings on the winding leg of the magnetic core, and including electrostatic shielding means disposed between the third winding and the first winding, and be tween the third winding and the second winding.

13. The elevator system of claim 8 wherein the winding leg of the magnetic core includes at least one nonmagnetic gap therein to prevent saturation of the magnetic core.

14. The elevator system of claim 1 wherein the first feedback means is a tachometer disposed to provide a signal responsive to the speed of the motor means, to which the speed of the car is responsive.

15. A motor control system for driving an elevator car, comprising:

a source of adjustable unidirectional potential,

a motor having an armature connected to said source of unidirectional potential, means providing a velocity command signal, first feedback means providing a first feedback signal responsive to the speed of the motor, comparator means providing an error signal respon- 1 sive to the difference between said first'feedback signal and said velocity'command signal, and means modifying saiderror signal to provide a stabilized error signal, including second feedback means providing a negative feedback signal responsive to the rate of change of counter emf developed by said motor, 7 said second feedback means developing said negative feedback signal statically and electromagnetically, without conductor continuity-between the armature of the motor and the circuit in which the negative feedback signal is developed, said source of unidirectional potential being responsive to the stabilized error signal. 16. The motor control system of claim 15 wherein the means providing the adjustable voltage source pro-- vides a unidirectional voltage with a ripple component, with the armature of the'motor means being connected to the adjustable voltage source.

17. The motor control system of claim 16 wherein the second feedback means includes means providing a first fl'ux responsive tothe adjustable voltage'source and the counter emf, means providing a second flux responsive to the adjustable voltage source, and means combining the'first and second fluxes to provide a substantially ripple-free resultant flux responsive to the rate of change of the counter emf.

18. The motor control system of claim 16 wherein the means providing the adjustable voltage source is a converter having static switching devices.

19. The motor control system of claim 15 wherein the second feedback means includes first and second windings disposed in inductive relation with a magnetic core, and magnetic field sensing means, said first winding being connected in a first circuit which includes the first winding connected in series with the armature of the motor means'across the adjustable voltage source, said second winding being connected across the adjustable voltage source in a second circuit which includes predetermined values of inductance and resistance, said magnetic field sensing means being disposed to develop an output voltage responsive to a changing difference between the fluxes developed in the magnetic core by said first and second windings.

20. The motor control system of claim 19 wherein the magnetic field sensing means includes a third, windmg.

21. The motor control system of claim 19 wherein the predetermined values of inductance and resistance in the circuit of the second winding are selected such that the total inductance and total resistance of the second circuit have substantially the same ratio to the total inductance and total resistance, respectively, of the first circuit, as the turn ratio'of the second to the first windings.

22. The motor control system of claim 20 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposed between the first and second end portions about which the first, second, and third windings are disposed.

23. The motor control system of claim 21 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposed between the first and second end portions, about which the first and second windings are disposed, and wherein the first winding is a predetermined fraction of one turn, with this fraction being used. to establish the ratio which guides the selection of the values of inductance and resistance in the second circuit. v f v 24. The motor'control system of claim 23 wherein the first winding includes electrical leads disposed to enter the chamber of the magnetic core through openings in a predetermined end thereof, with the first winding following a predetermined arcuate path between the electric leads, having a length responsive to the angular displacement of the leads, which angular displacement determines the specific fraction of a turn in the first winding. v

25. The motor control system of claim 20 wherein the third winding is disposed between the first and second windings on the winding leg of the magneticcore, and including electrostatic shielding means disposed between the third winding and the first winding, and between the third winding and the second winding.

26. The motor control system of claim 19 wherein the winding leg of the magnetic core includes at least one non-magnetic gap therein to prevent saturation of the magnetic core.

27. The motor control system of claim 15 wherein the first feedback means is a tachometer disposed to provide a signal responsive to the speed of the motor means, to which the speed of the car is responsive.

28. An acceleration transducer for providing a signal responsive to the acceleration of a direct current motor having an armature, comprising:

a magnetic core having a winding leg,

first and second windings disposed in inductive relation with said winding leg, magnetic field sensing means disposed ininductive relation with said winding leg,

said first winding being adapted for serial connection in a first circuit which includes the armature of the direct current motor,

said second winding being adapted for connection in a second circuit, which is connected across the first circuit,

the winding leg includes at least one non-magnetic gap therein. A v

30. The acceleration transducer of claim 28 wherein the acceleration transducer includes a magnetic enclosure surrounding the first and second windings and the magnetic field sensing means which interconnects the ends of the winding leg and functions as the return path for flux produced in the winding leg. 7

31. The acceleration transducer of claim 30 wherein the magnetic field sensing means includes a third winding disposed between the first and second windings on the winding leg, and including electrostatic shielding means disposed adjacent each end of the third winding.

32. The acceleration transducer of claim 28 including a magnetic housing having first and second ends and side wall portions defining a cavity, within which the winding leg, first and second windings and magnetic field sensing means are disposed, with the winding leg extending between the first and second ends of said magnetic housing.

33. The acceleration transducer of claim 32 wherein the first winding is less than a full turn, including elec trical leads which extend outwardly from the first winding through an end of the metallic enclosure. 

1. An elevator system, comprising: an elevator car, a structure having spaced landings to be served by said car, motor means including an armature, said motor means moving the car relative to said structure to serve the landings, means providing a speed pattern reference signal, first feedback means providing a first feedback signal, said first feedback signal being responsive to the speed of the car, means comparing the speed pattern reference signal with the first feedback signal to provide an error signal responsive to any difference, means stabiliziNg said error signal, including second feedback means, said second feedback means providing a negative feedback signal responsive to the rate of change of the counter emf of said motor means, said second feedback means developing said negative feedback signal statically and electromagnetically, without conductor continuity to the armature of the motor means, and means providing an adjustable voltage source responsive to said stabilized error signal, said motor means being connected to said adjustable voltage source.
 2. The elevator system of claim 1 wherein the means providing the adjustable voltage source provides a unidirectional voltage with a ripple component, with the armature of the motor means being connected to the adjustable voltage source.
 3. The elevator system of claim 2 wherein the second feedback means includes means providing a first flux responsive to the adjustable voltage source and the counter emf, means providing a second flux responsive to the adjustable voltage source, and means combining the first and second fluxes to provide a substantially ripple-free resultant flux responsive to the rate of change of the counter emf.
 4. The elevator system of claim 2 wherein the means providing the adjustable voltage source is a converter having static switching devices.
 5. The elevator system of claim 1 wherein the second feedback means includes first and second windings disposed in inductive relation with a magnetic core, and magnetic field sensing means, said first winding being connected in a first circuit which includes the first winding connected in series with the armature of the motor means across the adjustable voltage source, said second winding being connected across the adjustable voltage source in a second circuit which includes predetermined values of inductance and resistance, said magnetic field sensing means being disposed to develop an output voltage responsive to a changing difference between the fluxes developed in the magnetic core by said first and second windings.
 6. The elevator system of claim 5 wherein the magnetic field sensing means is a third winding disposed in inductive relation with the magnetic core.
 7. The elevator system of claim 5 wherein the predetermined values of inductance and resistance in the circuit of the second winding are selected such that the total inductance and total resistance of the second circuit have substantially the same ratio to the total inductance and total resistance, respectively, of the first circuit, as the turn ratio of the second winding to the first winding.
 8. The elevator system of claim 5 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposed between the first and second end portions about which the first and second windings are disposed.
 9. The elevator system of claim 8 wherein the magnetic field sensing means is a third winding, with said third winding being disposed about the winding leg.
 10. The elevator system of claim 7 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposed between the first and second end portions about which the first and second windings are disposed, and wherein the first winding is a predetermined fraction of one turn, with this fraction being used to establish the ratio which guides the selection of the values of inductance and resistance in the second circuit.
 11. The elevator system of claim 10 wherein the first winding includes electrical leads disposed to enter the chamber of the magnetic core through openings in a predetermined end thereof, with the first winding following a predetermined arcuate path between the electric leads, having a length responsive to the angular displacement of the leads, which angular displacement determines thee specific fraction of a turn in the first winding.
 12. The elevator systEm of claim 8 wherein the magnetic field sensing means is a third winding, said third winding being disposed between the first and second windings on the winding leg of the magnetic core, and including electrostatic shielding means disposed between the third winding and the first winding, and between the third winding and the second winding.
 13. The elevator system of claim 8 wherein the winding leg of the magnetic core includes at least one non-magnetic gap therein to prevent saturation of the magnetic core.
 14. The elevator system of claim 1 wherein the first feedback means is a tachometer disposed to provide a signal responsive to the speed of the motor means, to which the speed of the car is responsive.
 15. A motor control system for driving an elevator car, comprising: a source of adjustable unidirectional potential, a motor having an armature connected to said source of unidirectional potential, means providing a velocity command signal, first feedback means providing a first feedback signal responsive to the speed of the motor, comparator means providing an error signal responsive to the difference between said first feedback signal and said velocity command signal, and means modifying said error signal to provide a stabilized error signal, including second feedback means providing a negative feedback signal responsive to the rate of change of counter emf developed by said motor, said second feedback means developing said negative feedback signal statically and electromagnetically, without conductor continuity between the armature of the motor and the circuit in which the negative feedback signal is developed, said source of unidirectional potential being responsive to the stabilized error signal.
 16. The motor control system of claim 15 wherein the means providing the adjustable voltage source provides a unidirectional voltage with a ripple component, with the armature of the motor means being connected to the adjustable voltage source.
 17. The motor control system of claim 16 wherein the second feedback means includes means providing a first flux responsive to the adjustable voltage source and the counter emf, means providing a second flux responsive to the adjustable voltage source, and means combining the first and second fluxes to provide a substantially ripple-free resultant flux responsive to the rate of change of the counter emf.
 18. The motor control system of claim 16 wherein the means providing the adjustable voltage source is a converter having static switching devices.
 19. The motor control system of claim 15 wherein the second feedback means includes first and second windings disposed in inductive relation with a magnetic core, and magnetic field sensing means, said first winding being connected in a first circuit which includes the first winding connected in series with the armature of the motor means across the adjustable voltage source, said second winding being connected across the adjustable voltage source in a second circuit which includes predetermined values of inductance and resistance, said magnetic field sensing means being disposed to develop an output voltage responsive to a changing difference between the fluxes developed in the magnetic core by said first and second windings.
 20. The motor control system of claim 19 wherein the magnetic field sensing means includes a third winding.
 21. The motor control system of claim 19 wherein the predetermined values of inductance and resistance in the circuit of the second winding are selected such that the total inductance and total resistance of the second circuit have substantially the same ratio to the total inductance and total resistance, respectively, of the first circuit, as the turn ratio of the second to the first windings.
 22. The motor control system of claim 20 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposEd between the first and second end portions about which the first, second, and third windings are disposed.
 23. The motor control system of claim 21 wherein the magnetic core includes a substantially closed shell having a chamber defined by side wall and first and second end portions, and a winding leg disposed between the first and second end portions, about which the first and second windings are disposed, and wherein the first winding is a predetermined fraction of one turn, with this fraction being used to establish the ratio which guides the selection of the values of inductance and resistance in the second circuit.
 24. The motor control system of claim 23 wherein the first winding includes electrical leads disposed to enter the chamber of the magnetic core through openings in a predetermined end thereof, with the first winding following a predetermined arcuate path between the electric leads, having a length responsive to the angular displacement of the leads, which angular displacement determines the specific fraction of a turn in the first winding.
 25. The motor control system of claim 20 wherein the third winding is disposed between the first and second windings on the winding leg of the magnetic core, and including electrostatic shielding means disposed between the third winding and the first winding, and between the third winding and the second winding.
 26. The motor control system of claim 19 wherein the winding leg of the magnetic core includes at least one non-magnetic gap therein to prevent saturation of the magnetic core.
 27. The motor control system of claim 15 wherein the first feedback means is a tachometer disposed to provide a signal responsive to the speed of the motor means, to which the speed of the car is responsive.
 28. An acceleration transducer for providing a signal responsive to the acceleration of a direct current motor having an armature, comprising: a magnetic core having a winding leg, first and second windings disposed in inductive relation with said winding leg, magnetic field sensing means disposed in inductive relation with said winding leg, said first winding being adapted for serial connection in a first circuit which includes the armature of the direct current motor, said second winding being adapted for connection in a second circuit, which is connected across the first circuit, said first and second windings developing opposing fluxes in the winding leg, with the resultant flux linking said magnetic field sensing means, said magnetic field sensing means developing a voltage proportional to the rate of change of the resultant flux, which is responsive to the rate of change of the center emf of the motor and accelerator.
 29. The acceleration transducer of claim 28 wherein the winding leg includes at least one non-magnetic gap therein.
 30. The acceleration transducer of claim 28 wherein the acceleration transducer includes a magnetic enclosure surrounding the first and second windings and the magnetic field sensing means which interconnects the ends of the winding leg and functions as the return path for flux produced in the winding leg.
 31. The acceleration transducer of claim 30 wherein the magnetic field sensing means includes a third winding disposed between the first and second windings on the winding leg, and including electrostatic shielding means disposed adjacent each end of the third winding.
 32. The acceleration transducer of claim 28 including a magnetic housing having first and second ends and side wall portions defining a cavity, within which the winding leg, first and second windings and magnetic field sensing means are disposed, with the winding leg extending between the first and second ends of said magnetic housing.
 33. The acceleration transducer of claim 32 wherein the first winding is less than a full turn, including electrical leads which extend outwardly from the first winding through an end of the metallic enclosure. 